Image-display method, projector, image-display system, projector-control method, image-display program, and projector-control program

ABSTRACT

With a conventional image-display system, a presenter sometimes has difficulty in providing every viewer with an easy-to-see picture.  
     When projecting an image transmitted from a computer operated by the presenter and enabling the viewer to watch the image projected by the projector, the projector receives image data transmitted through two-way communication from the computer operated by the presenter, projects an image represented by the received image data and transmits the received image data to a client computer operated by the viewer through the two-way communication, and the client computer receives the image data transmitted through the two-way communication and displays the image represented by the received image data on its display.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to an image-display method, a projector,an image-display system, a projector-control method, an image-displayprogram, and a projector-control program.

[0003] 2. Description of the Related Art

[0004] In a conventional image-display system of this type, a presenterconnects his/her computer to a projector through a network and sends thedata of an image displayed on his/her computer to the projector, whichprojects the image on a screen (see, for example, Japanese UnexaminedPatent Publication No. 2001-14135).

[0005] With the above image-display system, the presenter sometimes hasdifficulty in providing every viewer with an easy-to-see picture. Forexample, viewers at a distance from the screen in a large presentationhall often have difficulty in watching the screen and concentrating onthe content of the presentation, particularly if letters and figures aresmall.

SUMMARY OF THE INVENTION

[0006] In accordance with the above, it is the object of the presentinvention to provide an image-display method, a projector, animage-display system, a projector-control method, an image-displayprogram, and a projector-control program capable of providing everyviewer with an easy-to-see picture.

[0007] To achieve the above object, image data transmitted from acomputer operated by a presenter are sent to client computers operatedby viewers according to the present invention. Because the image datarepresent images to be projected on a screen by a projector, viewers canwatch the images on the displays of client computers on hand byreproducing them with client computers. Accordingly, even if viewers areseated at a distance from the screen in a large hall, they can watchimages on the displays of client computers on hand.

[0008] Although it serves the purpose if the computer operated by thepresenter can transmit image data representing images to be projected ona screen, it is preferable if the computer operated by the presenter isthe same as the computer used by the presenter for presentation. In thissense, it is preferable to transmit image data for displaying computerpictures including the presenter's operation (operation of a mousepointer, etc.). Formats of image data are not limited in particular.Various formats such as picture signals, RGB signals, and compresseddata of MPEG etc. can be adopted.

[0009] It serves the purpose if the communication-control units of theprojector and the client computers can connect the computer operated bythe presenter and the client computers that can be operated by theviewers interactively, and communication lines, protocols and standardsare not limited. For example, either a wire network or a radio networkwill do, and various protocols such as TCP and UDP can be adopted, orvarious standards of Ethernet (a registered trademark of Fuji Xerox Co.,Ltd.), IEEE 1394, USB, etc. can be adopted.

[0010] It serves the purpose if the unit for projecting images canproject images represented by image data on a screen; accordingly, ifimage data are compressed, the projecting unit decompresses them andprojects images on a screen. The image data-transmitting section sendson the above image data received to client computers. If image data areprocessed (for example, expanded) for the display of images and thensent on to client computers, the image data become bulky and it takestime for the image data-transmitting section to send on the image datato client computers.

[0011] Accordingly, it is preferable for the image data-transmittingunit to send on the above image data received, just as they are, toclient computers. Besides, because image data are sent on from theprojector to client computers, it is unnecessary for the computeroperated by the presenter to be involved in the sending on of image datato a plurality of client computers. The load due to the control ofcommunication occurs on the projector alone. Because the computeroperated by the presenter is operated in various ways, the presenter canmake presentation smoothly even with a low-performance computer if extraloads are eliminated.

[0012] It serves the purpose if the image-displaying unit of the clientcomputer is capable of displaying the images represented by image datafed from the projector. If the above image-data processing is made inthe projector, it is preferable to do the processing and decompressing,etc. with the same algorithm so that images displayed on the displays ofclient computers are always the same as images displayed on the screenby the projector. If image data are stored in a hard disk, a RAM, or thelike of the client computer, the viewer can review images of thepresentation at any time. If a viewer cannot keep up with thepresentation, he/she can pause and restart at any time. Thus, suchconvenient functions can be achieved.

[0013] As described above, the projector sends on image datarepresenting projected images to the client computers so that viewerscan watch images on the displays of client computers. On the other hand,the presenter may want to disable the client computers from displayingcertain images because of the contents of the presentation orpresenter's intention. To achieve this selective non-display of image,the computer operated by the presenter sends the projector 30 dataindicating the permission or prohibition of the delivery of image datato the client computers, and the image data-transmitting unit of theprojector handles image data in accordance with thepermission/prohibition-indicating data. With regard todelivery-permitted image data, the projector permits all the clientcomputers, which demanded connection, to connect to itself and sends onthe image data to the client computers.

[0014] In this manner, the projector acquirespermission/prohibition-indicating data from the computer operated by thepresenter and handles image data in accordance with the presenter'sintention. Thus, by using permission/prohibition-indicating data alone,the projector can determine whether to send on image data to a pluralityof client computers or not. It is not necessary to control the deliveryor nondelivery of image data to individual client computers. Thus, thedelivery or nondelivery of image data to individual client computers canbe controlled by very simple processing.

[0015] The above delivery/nondelivery control is convenient especiallyfor the handling of image data in a presentation hall. In other words,because many viewers watch images in a presentation hall, it is oftennonsense to try to control the delivery and nondelivery of image data toindividual client computers. Accordingly, the delivery/nondeliverycontrol where the presenter takes the initiative in controlling deliveryand nondelivery is often sufficient.

[0016] The transmission of permission/prohibition-indicating data can bemade in various ways. The presenter may register the permission andprohibition of delivery of image data with the computer operated by thepresenter in advance, and the computer operated by the presenter mayautomatically transmit permission/prohibition-indicating data to theprojector in response to the inquiries from the projector. When thecomputer operated by the presenter receives an inquiry from theprojector, a pop-up menu for instruction of permission or prohibitionmay be displayed on the display of the computer operated by thepresenter.

[0017] To control the delivery or nondelivery of image data, passwordsto be inputted through client computers may be used. A viewer inputs apassword, which is visible to only the viewers of images projected onthe screen by the projector, into the image data-receiving unit ofhis/her client computer. When he/she demands connection to theprojector, the password is sent from his/her client computer to theimage data-transmitting unit and a password-checkup section determineswhether the password is correct or not. If the password is correct,image data are sent on to his/her client computer.

[0018] Thus, it is possible to determine whether image data should besent on to each client computer or not. Besides, because the password isvisible to only the viewers of images projected on the screen by theprojector, the destinations of image data can be limited to clientcomputers operated by the viewers of images projected on the screen bythe projector. Various passwords can be adopted as the password visibleto only the viewers of images projected on the screen by the projector.For example, a password may be written in images projected on the screenby the projector. Accordingly, the destinations of image data can belimited to client computers operated by the viewers in the presentationhall. Alternatively, slips printed with a password may be handed over tothe viewers at the entrance of the presentation hall.

[0019] Needless to say, the above image-display system functions by themethod of executing certain steps in time series with projector andclient computers; therefore, the image-display system constitutes aninvention as an image-display method and an projector-control method.The image-display system may exist by itself or may be incorporated intoa device. Thus, the image-display system as an idea of invention is notlimited to the above embodiment, but may be embodied in other specificforms. For example, the image-display system may be made of software ormay be made of hardware.

[0020] In the case of the embodiment of the idea of the invention assoftware for controlling an image-display system and a projector, thereexist programs realizing such functions, of course. The software isimage-display and projector-control programs which are executed in theprojector and client computers to realize the above functions.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a block diagram of an embodiment of the image-displaysystem of the present invention;

[0022]FIG. 2 is a flowchart of the processing by thetransmission-control program of the image-display system of FIG. 1;

[0023]FIG. 3 is a flowchart of the processing by the projector-controlprogram of the image-display system of FIG. 1;

[0024]FIG. 4 is a flowchart of the processing by the reception-controlprogram of the image-display system of FIG. 1; and

[0025]FIG. 5 is a schematic illustration of another embodiment ofimage-display system of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] The preferred embodiments of the present invention will bedescribed below in the following orders.

[0027] (1) Configuration of the image-display system

[0028] (2) Processing at the presenter PC

[0029] (3) Processing at the projector

[0030] (4) Processing at the client PCs

[0031] (5) Other embodiments

[0032] (1) Configuration of the Image-Display System

[0033]FIG. 1 shows a configuration of the image-display system of thepresent invention. The image-display system 10 comprises a presenter PC20, a projector 30, and a plurality of client PCs 40. The presenter PC20, projector 30, and client PCs 40 form a LAN through UTP cables andcan communicate with one another. The projector 30 receives image datafrom the presenter PC 20 and projects images on a screen. At the sametime, the projector 30 sends on the received image data as they are tothe client PCs 40 if the image data are delivery-permitted ones. Thus,the client PCs 40 receive image data from the projector 30 and displayimages on their displays.

[0034] The presenter PC 20, projector 30, and client PCs 40 communicatewith one another by using the TCP protocol. They send and receivepackets to and from one another to establish connection among them, andimage data are divided into packets for transmission as the need arises.There are block diagrams in FIG. 1 showing the configurations of apresenter PC 20, a projector 30, and only one client PC 40, but aplurality of client PCs 40 can be realized by using the sameconfiguration.

[0035] General-purpose computers can be adopted as a presenter PC 20 andclient PCs 40 which control certain interfaces and recording media undercertain operating systems. The presenter PC 20 of the image-displaysystem 10 of the present invention comprises a network interface 21, acommunication controller 22, a transmission-control program 23, ahard-disk drive 24, a presentation program 25, a displaying section 26,and an input device-controller 27.

[0036] To make presentation by using the projector 30, a presenteroperates the presenter PC 20 and starts the presentation program 25. Thepresentation program 25 reads out presentation data 24 a, which areprepared and stored in the hard-disk drive 24 in advance, and outputsimage data to the displaying section 26 to display images in certain orany order.

[0037] The displaying section 26 controls a display such as aliquid-crystal display (not shown in FIG. 1). A mouse 27 a or the likeinputs operation into the input device-controller 27, which outputs datarepresenting the contents of inputted operation to the presentationprogram 25, which makes processing such as changing the presentationpicture and moving the mouse pointer on the displaying section 26.

[0038] While the presentation program 25 is running, thetransmission-control program 23 is started and controls the transmissionof the image data representing the images on the presentation picture ofthe displaying section 26 to the projector 30 in order to make theprojector 30 project images on a screen which are the same as the imageson the presentation picture of the displaying section 26. Besides, thepresenter PC 20 is capable of achieving two-way communication by meansof the network interface 21 and the communication controller 22. Inother words, the communication controller 22 divides image dada fed fromthe transmission-control program 23 into packets as the need arises,makes such processing as adding data indicating proper destinations, andoutputs the image data through the network interface 21. Before beingtransmitted, image data may be compressed for a higher communicationspeed or encoded for security.

[0039] The transmission-control program 23 has adelivery/nondelivery-designating section 23 a. The displaying section 26and the input device-controller 27 constitute a user interface (notshown) under the control by the delivery/nondelivery-designating unit 23a. Thus, the presenter can designate the delivery and nondelivery ofimage data to the client PCs 40. The data representing the contents ofdesignation of delivery and nondelivery are stored in the hard-diskdrive 24 and can be referred to at any step. At the time of establishingthe communication with the projector 30 or at other times, a pop-up menumay be displayed on the user interface so that the presenter candesignate delivery or nondelivery of image data to the client PCs 40.And other various configurations for designation of delivery andnondelivery of image data are possible.

[0040] In the projector 30, certain interface, recording medium, etc.can be controlled under an operating system and a certain program can berun. To construct the image-display system 10, the projector 30comprises a network interface 31, a communication controller 32, aprojector-control program 33, a projection controller 34, and aprojecting section 35. The projector 30 is capable of two-waycommunication by means of the network interface 31 and the communicationcontroller 32. The communication controller 32 receives packets of imagedata through the network interface 31, combines the packets inaccordance with their headers, and sends the combined image data to theprojector-control program 33. Besides, the communication controller 32receives image data from the projector-control program 33, divides theimage data into packets as the need arises, makes such processing asadding data including proper destinations and outputs the packetsthrough the network interface 31.

[0041] The projector-control program 33 sends and receives image dataand controls the projection of images according to the received imagedata. Besides, the projector-control program 33 finds whether the imagedata received are delivery-permitted ones or delivery-prohibited onesand controls two-way communication with the client PCs 40. Moreover,when projecting images, the projector-control program 33 starts theprojection controller 34 and sends image data to it. The projectioncontroller 34 processes the received image data and controls theprojection of images at the projecting section 35.

[0042] Thus, the projection controller 34 processes the above image datareceived and produces data which are fed to the projecting section 35for the projection of images on a screen. If image data are compressedor encoded, the projection controller 34 decompresses or decodes theimage data. The projecting section 35 has a mechanism to project lightof three colors RGB on an external screen through a lens (not shown inFIG. 1) to form images. Thus, the projecting section 35 generates RGBlight for individual pixels to form images on the screen by using theabove image data processed by the projection controller 34.

[0043] In each client PC 40, certain interface, recording medium, etc.can be controlled under an operating system and a certain program can berun. To construct the image-display system of the present invention,each client PC 40 comprises a network interface 41, a communicationcontroller 42, a reception-control program 43, a display controller 44,and a displaying section 45. Each client PC 40 is capable of two-waycommunication by means of the network interface 41 and the communicationcontroller 42. The communication controller 42 receives packets throughthe network interface 41, combines the packets in accordance with theirheaders, and sends the combined image data to the reception-controlprogram 43.

[0044] The reception-control program 43 receives and sends image dataand controls the display of images according to the received image data.To receive image data, the reception-control program 43 controls two-waycommunication with the projector 30. The reception-control program 43starts the display controller 44 and sends the image data to it. Thedisplay controller 44 processes the image data and controls the displayof images at the displaying section 45. Thus, the display controller 44processes the above image data received and produces data to be sent tothe displaying unit 45 for the display of images. The displaying section45 has a display such as a liquid-crystal display (not shown in FIG. 1)and generates RGB light for individual pixels to form images on thedisplay.

[0045] The processing at the display controller 44 is equivalent to theprocessing at the projection controller 34. If image data are compressedor encoded, the display controller 44 decompresses or decodes the imagedata by using the same algorithm as the projection controller 34.Because the projector 30 projects images on a screen while the client PC40 displays images on a display, the projection controller 34's methodof driving the relevant parts for the projection of images is differentfrom the display controller 44's method of driving the relevant partsfor the display of images. In this embodiment, however, the projectioncontroller 34 and the display controller 44 have a common point in thatan image is expressed by pixels of RGB colors. Thus, the method ofprocessing image data is common to the two controllers 34 and 44.Therefore, the projector 30 and the client PCs 40 have many commonmodules and hence the image-display system 10 of the present inventioncan be constructed easily.

[0046] (2) Processing at the Presenter PC

[0047] The processing and workings of the presenter PC 20 are nowdescribed. FIG. 2 is a flowchart of the processing of thetransmission-control program 23 of the presenter PC 20. In thisembodiment, the presenter PC 20 communicates with the projector 30 anddoes not communicate with the client PCs 40. In Step S100, thetransmission-control program 23 demands connection to the projector 30of the communication controller 22. The communication controller 22transmits a connection-demanding packet to the projector 30 through thenetwork interface 21. In Step S110, the transmission-control program 23monitors the network interface 21 through the communication controller22 for a connection-permitting packet from the projector 30.

[0048] When the communication controller 22 receives aconnection-permitting packet from the projector 30, thetransmission-control program 23 recognizes the permission in Step S110and monitors the network interface 21 further through the communicationcontroller 22 to find whether there is a demand for the delivery ofimage data or not in Step S120. In other words, the transmission-controlprogram 23 monitors the network interface 21 for a delivery-demandingpacket from the projector 30. If a demand for the delivery of image datais not found in Step S120, the transmission-control program 23 checks tosee if a preset time has passed in Step S125. The transmission-controlprogram 23 repeats the processing in and after Step S120 until thepreset time passes.

[0049] If the preset time has passed without receiving adelivery-demanding packet in Step S125, thedelivery/nondelivery-designating section 23 a designates image data asdelivery-prohibited data and makes the communication controller 22transmit a datum indicating the prohibition of delivery to the projector30 in Step S140. If delivery of image data is demanded in Step S120, thedelivery/nondelivery-designating section 23 a checks in Step S130 to seeif the delivery is already permitted. If it is found in Step 130 thatthe delivery is not permitted, the delivery/nondelivery-designatingsection 23 a makes the communication controller 22 transmit a datumindicating the prohibition of delivery to the projector 30 in Step S140.

[0050] If it is found in Step S130 that the delivery is permitted, thedelivery/nondelivery-designating unit 23 a makes the communicationcontroller 22 transmit a datum indicating the permission of delivery tothe projector 30 in Step S135. In Step 150, the image data representinga presentation image displayed on the displaying section 26 under thecontrol by the presentation program 25 are transmitted to the projector30. Before the transmission, the image data are compressed or encoded asthe need arises. In Step S160, the transmission-control program 23checks to see if the presentation has been finished. The processing inand after Step S150 is repeated until the presentation is finished.

[0051] By the processing described above, image data representing thepresentation images to be projected by the projector 30 are outputtedfrom the presenter PC 20. Besides, the presenter PC 20 designates imagedata as ones to be delivered from the projector 30 to the client PCs 40and ones not to be delivered from the projector 30 to the client PCs 40and transmits data indicating the contents of the designation to theprojector 30. It serves the purpose if the data indicating the contentsof designation are transmitted to the projector 30 only once. Thus, thesubstantial communication load on the system is only the imagedata-transmission load. Accordingly, when the presenter makespresentation, operating the presenter PC 20, the resource of thepresenter PC 20 is prevented from being reduced and hence the presentercan make presentation very smoothly.

[0052] (3) Processing at the Projector

[0053]FIG. 3 is a flowchart of the processing of the projector-controlprogram 33 of the projector 30. In this embodiment, the projector 30makes two-way communication with the presenter PC 20 and the client PCs40. In Step S200, the projector-control program 33 checks to see if thenetwork interface 31 has received a demand for connection through thecommunication controller 32. In other words, the projector-controlprogram 33 monitors the network interface 31 through the communicationcontroller 32 for a connection-demanding packet to be outputted by thepresenter PC 20 in Step S100.

[0054] If the reception of a connection-demanding packet was confirmedin Step S200, the projector-control program 33 makes the communicationcontroller 32 transmit a connection-permitting packet through thenetwork interface 31 to the presenter PC 20 in Step S210. In Step S220,the projector-control program 33 makes the communication controller 32transmit a delivery-demanding packet through the network interface 31 tothe presenter PC 20 in order to check to see if the delivery of imagedata to the client PCs 40 is permitted.

[0055] The presenter PC 20 recognizes the demand of delivery in StepS120 and transmits a datum indicating the permission of delivery in StepS135 or a datum indicating the prohibition of delivery in Step S140 tothe projector 30. The projector 30 monitors the network interface 31through the communication controller 32 for a datum indicating thepermission or prohibition of delivery in Step S225. If theprojector-control program 33 finds in Step S225 that the delivery ofimage data to the client PCs 40 is permitted, the projector-controlprogram 33 designates image data as delivery-permitted ones in StepS230. If the projector-control program 33 finds in Step S225 that thedelivery of image data to the client PCs 40 is prohibited, theprojector-control program 33 designates image data asdelivery-prohibited ones in Step S235. Various configurations can beadopted for the designation. For example, flags indicating thepermission and prohibition of delivery may be stored in a RAM (not shownin FIG. 1).

[0056] When image data has been designated as delivery-permitted ordelivery-prohibited ones, the projector-control program 33 makes thecommunication controller 32 monitor the network interface 31, receivethe image data representing a presentation image, and store the imagedata temporarily in a RAM (not shown in FIG. 1) in Step S240. In otherwords, the projector-control program 33 makes the communicationcontroller 32 receive packets of image data, combine the packets, andstore the combined image data in a RAM. In Step S245, the received imagedata are sent to the projection controller 34 for the projection of thepresentation image. In other words, the projection controller 34processes (decompresses or decodes as the need arises) the compressed orencoded image data temporarily stored in the RAM to produce data whichthe projecting section 35 uses to project the presentation image.

[0057] In Step S250, the projector-control program 33 checks to seewhether image data are designated as delivery-permitted ones (in StepS230) or not (in Step S235). If it is confirmed in Step S250 that imagedata are designated as delivery-permitted ones, the projector-controlprogram 33 monitors the network interface 31 through the communicationcontroller 32 for connection-demanding packets from client PCs 40 inStep S255. If it is confirmed in Step S255 that some client PCs 40 havesent connection-demanding packets to the projector 30, theprojector-control program 33 permits the connection-demanding client PCs40 to connect with the projector 30 in Step S260. In other words, theprojector-control program 33 makes the communication controller 32transmit a packet indicating the permission of connection to theconnection-demanding client PCs 40 through the network interface 31.

[0058] In Step S265, the projector-control program 33 sends the imagedata temporarily stored in the RAM to the connection-permitted clientPCs 40. In other words, the projector-control program 33 makes thecommunication controller 32 (i) divide the image data into packets, (ii)write data, which address the packets to the connection-permitted clientPCs 40, into the headers of packets, and (iii) transmit the packetsthrough the network interface 31 to the connection-permitted client PCs40. The image data sent to the connection-permitted client PCs 40 arethe same as the image data stored in the above RAM. In other words, theimage data stored in the RAM are transmitted, just as they are, withoutundergoing the processing by the projection controller 34, to theconnection-permitted client PCs 40; therefore, if the image data storedin the RAM is compressed, the image data can be transmitted as arelatively light load on the network.

[0059] If the image data were transmitted to the connection-permittedclient PCs 40 in Step S265 or any client PCs 40 did not sendconnection-demanding packets to the projector 30 in Step S255, theprojector-control program 33 checks in Step S270 to see if thepresentation has been finished. In other words, the projector-controlprogram 33 makes the communication controller 32 monitor the networkinterface 31 and finds whether the final presentation image has beenreceived or not. The processing in and after Step S240 is repeated untilthe ending of the presentation is confirmed in Step S270. If image datawere designated as delivery-prohibited ones in Step S250, theprojector-control program 33 checks in Step S275 to see if thepresentation has been finished. If the ending of the presentation is notconfirmed in Step S275, the processing in and after Step S240 is made.

[0060] As described above, the projector 30 not only receives image datafrom the presenter PC 20 and projects images on a screen but also sendson image data to connection-permitted client PCs 40 if image data aredesignated as delivery-permitted ones. Because the projector 30communicates with the client PCs 40 and sends image data to the clientPCs 40, the load on the presenter PC 20 is very light. Besides, becausethe projector 30 receives image data from the presenter PC 20 and sendson the image data just as they are to the client PCs 40, no load ofimage processing occurs on the projector 30 and image data are smoothlysent to the client PCs 40 where the viewers can watch images clearly.

[0061] RGB cables, coaxial cables, etc. are known as technologies usedfor the transmission of image data. To transmit image data by usingthese technologies for the projection of images by the projector 30, twolines are needed; i.e., one line of, for example, RGB for thetransmission of image data and another line for two-way communicationfor the control of the relevant devices. In the present embodiment ofthis invention, however, it serves the purpose if a cable network isformed among the presenter PC 20, the projector 30 and the client PCs40. Thus, the image-display system 10 can be constructed with relativelysimple construction.

[0062] (4) Processing at the Client PC

[0063]FIG. 4 is a flowchart of the processing of the reception-controlprogram 43 of the client PCs 40. The client PCs 40 communicate with theprojector 30 and not with the presenter PC 20. In Step S300, thereception-control program 43 sends a demand for connection to theprojector 30 through the communication controller 42. In other words,the reception-control program 43 makes the communication controller 42send a packet indicating a demand for connection to the projector 30through the network interface 41.

[0064] In Step 310, the reception-control program 43 finds if theconnection is permitted. In other words, the reception-control program43 monitors the network interface 41 through the communicationcontroller 42 to find if a connection-permitting packet to betransmitted by the projector 30 in Step S260 has been received. If thereception-control program 43 finds in Step S310 that the connection ispermitted, the reception-control program 43 receives image dataoutputted by the projector 30 in Step S320. In other words, thereception-control program 43 makes the communication controller 42 (i)monitor the network interface 41, (ii) receive the packets of image datarepresenting a presentation image, (iii) combine the packets into theoriginal image data, and (iv) store the image data in a RAM (not shownin FIG. 1) temporarily.

[0065] In Step S340, the reception-control program 43 sends the imagedata to the display controller 44 for the display of the presentationimage on the display. In other words, the display controller 44processes (decompresses or decodes as the need arises) the decompressedor encoded image data to produce data which the displaying section 45uses to display the presentation image. Then, in Step S340, thereception-control program 43 makes the communication controller 42monitor the network interface 41 to find if the final presentation imagehas been received. Thus, the processing in and after step S320 isrepeated until the ending of the presentation is confirmed.

[0066] If the reception-control program 43 does not find in Step S310that the connection is permitted, the processing in and after Step 320is skipped and image data are not received. As described above, theclient PC 40 receives image data from the projector 30 and displays thepresentation image on its display. Accordingly, even if viewers areseated at a distance from the screen in a large hall, they can watchimages on the display of client computers on hand.

[0067] (5) Other Embodiments

[0068] The embodiment described above is an example to achieve theimage-display system, projector, image-display method, projector-controlmethod, image-display program and projector-control program of thepresent invention, and other configurations are also possible. Forexample, the destinations of image data maybe limited to client PCs 40operated by the participants, or viewers, in the presentation hall. Forexample, the projector permits all the client PCs 40, which demandedconnection, to connect to itself and sends on the image data to them.However, passwords to be inputted through client computers may be usedto control the delivery of image data.

[0069] The descriptions surrounded by broken lines in FIGS. 3 and 4 showthe processing to be added when the passwords are used to control thedelivery of image data, and FIG. 5 is a schematic diagram showingworkings of such an example. In this example, as shown in FIG. 5 as animage projected on the screen by the projector 30, a password isdisplayed in a part of the presentation image. Therefore, the image datasent from the presenter PC 20 are data including an image for displayingthe password, and the projector 30 displays the password when projectingthe image on the screen in Step S245.

[0070] At the client PC 40, the password is inputted by an input devicesuch as a keyboard before sending a demand for connection in Step S300.When sending the demand for connection in Step S300, together with dataindicating the demand for connection, data indicating the password issent. Before giving permission to the connection-demanding client PC 40in Step S260, the projector 30 acquires the inputted data indicating thepassword and determines whether the password is correct or not. When itis found that the password is correct, the demand for connection ispermitted in Step S260. When it is found that the password is notcorrect, the processing in Step S270 is carried out.

[0071] There are various ways to determine whether the password iscorrect or not. For example, data indicating the correct password may bestored in advance temporarily in a RAM, etc. (not shown) of theprojector 30 and the inputted password may be compared with the storedcorrect password. Further, the data of the password included in theimage data received in the above Step S240 may be extracted and used asthe correct password, and various other ways are also possible. Eitherof the above configurations enables viewers of the image projected onthe screen in the presentation hall to input the correct passwords, sothat the destinations of image data can be limited to client PCs 40 inthe presentation hall.

What is claimed is:
 1. An image-display method of projecting an imagetransmitted from a computer operated by a presenter on a screen by aprojector and enabling a viewer to watch the image projected by theprojector, wherein the projector receives image data transmitted fromthe computer operated by the presenter through two-way communication,projects the image represented by the received image data, and transmitsthe received image data to a client computer operated by the viewerthrough the two-way communication, and wherein the client computerreceives the transmitted image data through the two-way communicationand displays the image represented by the received image data on itsdisplay.
 2. The image-display method according to claim 1, wherein theprojector receives data indicating permission or prohibition of deliveryof the image data transmitted from the computer operated by thepresenter through the two-way communication and transmits the image datato the client computer when receiving delivery-permitting data for theimage data.
 3. The image-display method according to claim 2, whereinthe client computer demands connection to the projector and theprojector permits the client computer to connect to itself and sends onthe image data when receiving the delivery-permitting data for the imagedata.
 4. The image-display method according to claim 3; wherein theclient computer accepts a password visible to only the viewer of theimage projected on the screen by the projector and sends the acceptedpassword when demanding the connection to the projector, and wherein theprojector receives the password sent from the client computer to find ifthe password is correct and sends the image data when the password isfound correct.
 5. The image-display method according to claim 1, whereinthe projector transmits the received image data just as they are to theclient computer and wherein the client computer decompresses the imagedata by using the same algorithm as the projector and displays the imageon its display.
 6. A projector projecting an image transmitted from acomputer operated by a presenter and enabling a viewer to watch theprojected image, the projector comprising: a communication-control unitof the projector conducting two-way communication with externalcomputers; an image data-receiving unit of the projector receiving imagedata transmitted from the computer operated by the presenter through thecommunication-control unit of the projector; an image-projecting unitprojecting an image represented by the received image data; and an imagedata-transmitting unit transmitting the image data received through thecommunication-control unit of the projector to a client computeroperated by the viewer.
 7. An image-display system capable of having aprojector project an image transmitted from a computer operated by apresenter and enabling a viewer to watch the image projected by theprojector: wherein the projector comprises a communication-control unitof the projector conducting two-way communication with externalcomputers, an image data-receiving unit of the projector receiving imagedata transmitted from the computer operated by the presenter through thecommunication-control unit of the projector, an image-projecting unitprojecting an image represented by the received image data, and an imagedata-transmitting unit transmitting the image data received through thecommunication-control unit of the projector to a client computeroperated by the viewer; and wherein the client computer comprises acommunication-control unit of the client computer conducting two-waycommunication with the projector, an image data-receiving unit of theclient computer receiving the image data transmitted through thecommunication-control unit of the client computer, and animage-displaying unit displaying the image represented by the receivedimage data on its display.
 8. A projector-control method of projectingan image transmitted from a computer operated by a presenter andenabling a viewer to watch the projected image; wherein image datatransmitted from the computer operated by the presenter are receivedthrough two-way communication, an image represented by the receivedimage data is projected, and the received image data are transmittedthrough the two-way communication to a client computer operated by theviewer.
 9. An image-display program capable of having a projectorproject an image transmitted from a computer operated by a presenter andenabling a viewer to watch the image projected by the projector: whereinthe projector is provided with a communication-control function of theprojector conducting two-way communication with external computers, animage data-receiving function of the projector receiving image datatransmitted from the computer operated by the presenter through thecommunication-control function of the projector, an image-projectingfunction projecting an image represented by the received image data, andan image data-transmitting function transmitting the image data receivedthrough the communication-control function of the projector to a clientcomputer operated by the viewer; and wherein the client computer isprovided with a communication-control function of the client computerconducting two-way communication with the projector, an imagedata-receiving function of the client computer receiving the image datatransmitted through the communication-control function of the clientcomputer, and an image-displaying function displaying the imagerepresented by the received image data on the display.
 10. Aprojector-control program projecting an image transmitted from acomputer operated by a presenter and enabling a viewer to watch theprojected images, the projector-control program providing a controlcomputer of a projector with; a communication-control function of theprojector conducting two-way communication with external computers, animage data-receiving function of the projector receiving image datatransmitted from the computer operated by the presenter through thecommunication-control function of the projector, an image-projectingfunction projecting an image represented by the received image data, andan image data-transmitting function transmitting the image data receivedthrough the communication-control function of the projector to a clientcomputer operated by the viewer.